It is known that separate documents of the letter and envelope type may be combined with the help of automatic machines which fold up the letter paper, open the envelope, insert the folded-up letter in the envelope and then seal the envelope with the letter inside.
It is also known that machines of the abovementioned type may be combined with devices for imprinting the name and address of the envelope as well as the letter. However, the printing of the envelope can be avoided through use of window envelopes which permit the address imprinted on the letter to be visible through the transparent window of the envelope.
In certain cases it is desirable to distribute more personally formulated letters in mass edition, which can be done with the help of modern techniques. Even though such letters contain a large amount of standard text, they will yet include parts directed just to the person to whom the letter is addressed. In the case of such personalized letters it is of great importance that the "right letter reach the right person". The use of so-called window envelopes is considered undesirable in the case of personalized letters and instead the use of envelopes with the address written thereon is perferred, since this underlines the personal character of the letter. The technical problem is to ensure that the right letter is combined with the right addressee. In principle, known devices exist by means of which such a combination can be arrived at with great safety. This can be achieved, for example, by providing the letter as well as the envelope with an electronically readable bar code that corresponds to the name and address of the addressee. However the presence of such a bar code takes away from the personal character of the letter and for this reason, bar code markings are oftentimes avoided.